This invention relates generally to a liquid crystal display (LCD), and more particularly to an LCD display utilizing miniaturized pixel cells having shared active regions.
For many decades, the cathode ray tube (CRT) was the dominant display device creating an image by scanning a beam of electrons across a phosphor-coated screen causing the phosphors to emit visible light. The beam is generated by an electron gun and is passed through a deflection system that causes the beam to rapidly scan left-to-right and top-to-bottom. A magnetic lens focuses the beam to create a small moving dot on the phosphor screen. This rapidly moving spot of light paints an image on the surface of the viewing screen.
Light emitting diodes (LEDs) have also found a multitude of uses in the field of optoelectronics. An LED is a solid-state device capable of converting a flow of electrons into light. By combining two types of semiconductive material, LEDs emit light when electricity is passed through them. Displays comprised of LEDs may be used to display a number of digits each having seven segments. Each segment consists of a group of LEDs, which in combination can form alphanumeric images. They are commonly used in, for example, digital watch displays, pager displays, cellular handset displays, etc., and due to their excellent brightness, LEDs are often used in outdoor signs. Generally speaking, however, they have been used primarily in connection with non-graphic, low-information-content alphanumeric displays. In addition, in a low-power CMOS digital system, the dissipation of LEDs or other comparable display technology can dominate the total system""s power requirements, which could substantially negate the low-power dissipation advantage of CMOS technology.
Liquid crystal displays (LCDs) were developed in the 1970s in response to the inherent limitations in the then existing display technologies (e.g. CRTs, LED displays, etc.) such as excessive size, limited useful life, excessive power consumption, and limited information content. LCD displays comprise a matrix of pixels that are arranged in rows and columns that can be selectively energized to form letters or pictures in black and white or in a wide range of color combinations. An LCD modifies light that passes through it or is reflected from it as opposed to emitting light, as does an LED. An LCD generally comprises a layer of liquid crystalline material suspended between two glass plates or between a glass plate and a substrate. A principle advantage of an LCD over other display technologies is the ability to include thousands or even millions of pixels in a single display paving the way for much greater information content.
With the shift from segmented, very low information content displays to more information-rich digital products, LCDs now appear in products throughout the communications, office automation, and industrial, medical, and commercial electronics industries. Historically, the market for small displays has demanded low cost, minimal power consumption, and high image quality. It is well known that image quality is improved as display resolution increases, and that this can be accomplished by increasing the size of the array for a fixed pixel cell size. Unfortunately, system costs increase dramatically as the diagonal length of the array increases. It is also known that the stored video voltage on each pixel cell capacitor is subject to noise signals due to capacitive coupling between adjacent rows and columns. Capacitively coupled noise signals on the pixel will result in an image which does not correctly match the stored video signal, and therefore image quality is degraded. Increasing the physical separation between the pixel cell capacitor metal interconnect and the row and column line reduces capacitive coupling but has the undesirable effect of requiring a larger pixel cell die area to maintain a fixed capacitance.
In view of the foregoing, it should be appreciated that it would be desirable to increase the display resolution of an LCD display without increasing display size. Furthermore, it would likewise be desirable to minimize unwanted capacitive coupling between each pixel cell capacitor and adjacent rows and columns. Additional desirable features will become apparent to one skilled in the art from the foregoing background of the invention and the following detailed description of a preferred exemplary embodiment and appended claims.
In accordance with the teachings of the present invention, there is provided an LCD pixel device of the type deployed in a matrix of pixels that are selectively energized by a plurality of row lines and plurality of column lines and wherein a video voltage is stored on at least one pixel capacitor and coupled to an image-generating device. First and second source regions are formed near the surface of a semiconductor substrate. A drain region is likewise formed in the substrate between the first and second source regions forming the channels of first and second field-effect-transistors. An insulating layer is formed on the substrate, and first and second gate electrodes are provided in the insulating layer between the first source region and the drain region and between the second source region and the drain region, respectively. First and second mirrors are provided on the surface of the insulating layer. Conductive interconnects formed in the insulating layer provide electrical coupling between the first and second transistors, the first and second capacitors, and the first and second mirrors, respectively.